1. Technical Field
The present invention relates to a printing apparatus discharging liquid drops to perform printing, a control method for a printing apparatus, and a control program for a printing apparatus.
2. Related Art
A printing apparatus that forms a print target such as an image on a medium such as paper with ink discharged from nozzles may not normally discharge ink from the nozzles because of thickening or the like of ink. When an abnormal discharge that is a state where ink cannot be normally discharged from a nozzle occurs, that is, when the state of the discharged ink is abnormal, a dot that is supposed to be formed by the ink discharged from the nozzle is not formed, and this degrades the quality of the print target formed on the medium. In order to suppress such quality degradation due to failure of dot formation, there are suggested various types of technology in which when an abnormal discharge occurs in one nozzle, another nozzle discharges ink to form a dot instead of discharging ink from the one nozzle. That is, technologies for complementing one nozzle in which an abnormal discharge occurs with another nozzle are suggested.
In JP-A-9-024609, for example, there is suggested a technology for complementing one nozzle with another nozzle when an abnormal discharge occurs in one nozzle, by increasing the amount of ink discharged from another nozzle that is adjacent to the one nozzle.
In JP-A-2004-174816, there is suggested a technology for complementing one nozzle with another nozzle when an abnormal discharge occurs in one nozzle discharging ink of one color, by increasing the amount of ink discharged from another nozzle that discharges ink of another color.
The above printing apparatus performs discharge state inspection that is an inspection of whether an abnormal discharge occurs in a nozzle. Generally, such discharge state inspection is performed between a printing process performed on one medium and a printing process performed on the medium subsequent to the one medium when a print target is formed on a plurality of media. At this time, in order to reduce load on the printing apparatus necessitated by determination of whether an abnormal discharge occurs as well as complementation based on the determination result, determination of a discharge state is performed on a part of a plurality of discharging units, each including one nozzle, in one instance of the discharge state inspection. Each time one instance of the discharge state inspection is performed, the inspection target discharging unit changes in order. When a plurality of instances of the discharge state inspection elapses, the rounds of the inspection target discharging units are made, and determination of the discharge state of all of the discharging units is completed. When the rounds of the inspection target discharging units are made, determination of a discharge state is again repeated for each discharging unit in the same order.
For example, when the printing apparatus is configured to include individual discharging units for black, cyan, magenta, and yellow, a discharging unit that discharges black ink is targeted for inspection in the first discharge state inspection, and a discharging unit that discharges cyan ink is targeted for inspection in the second discharge state inspection. In addition, a discharging unit that discharges magenta ink is targeted for inspection in the third discharge state inspection, and a discharging unit that discharges yellow ink is targeted for inspection in the fourth discharge state inspection. Then, the discharge state of the discharging unit is repeatedly determined in the order of the black discharging unit, the cyan discharging unit, the magenta discharging unit, and the yellow discharging unit.
As such, determination of the discharge state of one discharging unit is performed only once in each of a plurality of instances of the discharge state inspection for one of the color discharging units. Therefore, when, for example, an abnormal discharge occurs in the black discharging unit immediately after the discharge state thereof is determined in the first discharge state inspection in the above example, the abnormal discharge is not detected until the fifth discharge state inspection. In addition, a dot that is supposed to be formed by the discharging unit where the abnormal discharge is detected is omitted until a complementation process or a maintenance process is performed on the discharging unit where the abnormal discharge is detected, and printing continues with degraded image quality.
Particularly, when a general paper such as a document is formed, there is ink that is frequently used in forming a print target, such as black ink. If an abnormal discharge occurs in a discharging unit that discharges such frequently used ink and the absence of either a complementation process or a maintenance process continues, formation of a print target continues in a state where image quality is significantly degraded, thereby causing wasteful consumption of a medium.